HCPL-7720 Datasheet, PDF(14/18 Page) Agilent(Hewlett-Packard) – 40 ns Propagation Delay CMOS Optocoupler

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HCPL-7720 Datasheet, PDF (14/18 Pages) Agilent(Hewlett-Packard) – 40 ns Propagation Delay CMOS Optocoupler

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Implementing DeviceNet and SDS

with the HCPL-772X/072X

With transmission rates up to 1

Mbit/s, both DeviceNet and SDS

are based upon the same

broadcast-oriented, communica-

tions protocol â the Controller

Area Network (CAN). Three types

of isolated nodes are

recommended for use on these

networks: Isolated Node Powered

by the Network (Figure 18),

DRAIN/SHIELD

SIGNAL

POWER

NODE/APP SPECIFIC

uP/CAN

HCPL

772x/072x

HCPL

772x/072x

TRANSCEIVER

REG.

ISOLATED

SWITCHING

POWER

SUPPLY

GALVANIC

ISOLATION

BOUNDARY

V+ (SIGNAL)

Vâ (SIGNAL)

V+ (POWER)

Vâ (POWER)

Isolated Node with Transceiver

Powered by the Network (Figure

19), and Isolated Node Providing

Power to the Network (Figure 20).

Isolated Node Powered by the

Network

This type of node is very flexible

and as can be seen in Figure 18, is

regarded as âisolatedâ because not

all of its components have the

same ground reference. Yet, all

components are still powered by

the network. This node contains

two regulators: one is isolated and

powers the CAN controller, node-

specific application and isolated

(node) side of the two optocoup-

lers while the other is non-

isolated. The non-isolated

regulator supplies the transceiver

and the non-isolated (network)

half of the two optocouplers.

NETWORK

POWER

SUPPLY

Figure 18. Isolated node powered by the network.

Isolated Node with Transceiver

Powered by the Network

Figure 19 shows a node powered

by both the network and another

source. In this case, the trans-

ceiver and isolated (network) side

of the two optocouplers are

powered by the network. The rest

of the node is powered by the AC

line which is very beneficial when

an application requires a

significant amount of power. This

method is also desirable as it does

not heavily load the network.

More importantly, the unique

âdual-invertingâ design of the

HCPL-772X/072X ensure the

network will not âlock-upâ if

either AC line power to the node

is lost or the node powered-off.

Specifically, when input power

(VDD1) to the HCPL-772X/072X

located in the transmit path is

eliminated, a RECESSIVE bus

state is ensured as the

HCPL-772X/072X output voltage

(VO) go HIGH.

*Bus V+ Sensing

It is suggested that the Bus V+

sense block shown in Figure 19 be

implemented. A locally powered

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